I’ve tested the AMP and regular versions of a The Guardian article page, and the AMP version is more than 4 times smaller in terms of transferred KBs, coming in at about 300 KB. Yes, JavaScript represents more than half of that size, and there are 16 separate script files, but in comparison to the regular page, it’s a significant improvement.
The funny thing is that that Guardian article page is probably less then 10Kb in content to begin with. It's all the cruft on the page that makes it large, and AMP is also cruft, just less of it.
I was implying that AMP leads to a reduction of JS in practice. Of course, if you have a very simple blog which loads very little JS to begin with, AMP could make things “worse.” But these types of blogs are an exception—unfortunately.
Note: I’ve tested with an ad/tracking blocker.